Idle issue

almost everytime I shift into neutral to coast to a stop the idle goes up. sometimes as high as 2500+ where it'll hang for a couple seconds (until i come to a complete stop) before returning to the normal level. I haven't gotten any check engine lights and the last time I brought it in for an oil change the guy said that it was normal and caused by the ac kicking on. so i did a little test and drove with the ac off and still had the problem. Any ideas what the problem is? it quite annoying idling at 2500 at a stop light with everyone looking at you. also the car is 05, v6, 5speed.

edit: sorry I realize there is a more specific forum for this.

Last edited by mtbiker; 07-22-2009 at 12:13 PM.
Reason: I realize there is a more specific forum for this

I am in the process of resetting the computer, folloing ohios advice. I just detached the battery for 30 mins, and now its idling. After reattaching the battery the speedometer is now correctly aligned. its been severly misaligned for a while. so one problems fixed.

well the excitement was short lived after a 10 mile ride. still having the rpm problem and the speedometer kept climbing everytime i hit the gas and never went down so the pointer is in a 6 o clock position.

Clutch in and come to a stop. Shift into 1st gear while waiting for the light. No need to shift into neutral. I've driven manual for over 30 years and only shifted into neutral to coast if my left foot itched or my sock needed to be pulled up.